A duplex unit is a device which enables transmission and reception of radio signals using a single antenna arrangement. Such transmission and reception is often referred to as duplexing. Radio communications systems in general, and microwave communications systems in particular have traditionally utilized so-called frequency duplexing, i.e. using separated transmit and receive frequency bands, as a means to separate an often comparably weak received radio signal from a comparably strong transmitted signal. However, frequency duplexing is wasteful in terms of frequency spectrum, since the frequency bands used by each of the transmit signal and the receive signal may not overlap.
The total number of antennas used by a communication system, particularly by a microwave communication system, is an important aspect which contributes to the total cost of the communication system. Hence, all other things being equal, a communication system which only uses a single antenna arrangement per transceiver is preferred over a communications system which utilizes a plurality of antenna arrangements at each transceiver.
In the article “Achieving Single Channel, Full Duplex Wireless Communication”, J. Choi, M. Jain, K. Srinivasan, P. Levis, and S. Katti, Proc. MobiCom'10, Sep. 20-24, 2010, Chicago, Ill., U.S.A., there is disclosed a system for simultaneous reception and transmission of radio signals in overlapping frequency bands. However, the system disclosed in this document needs at least three separate antennas in order to enable the reception and transmission of radio signals in overlapping frequency bands.